The present invention relates to a method of detecting defective pixels produced in a solid-state image-pickup device such as a charge-coupled device (CCD) used in a television camera and more particularly to a defective pixel detecting method and an image-pickup apparatus having a defective pixel correcting function using the detecting method capable of detecting in real time whether any defective pixel occurs in any image-pickup device or not in the image-pickup apparatus having a plurality of image-pickup devices and in which incident light from an imaging field is separated into R, G, B spectral components respectively and the spectral lights are imaged by the plurality of image-pickup devices.
A conventional method of detecting defective pixels in solid-state image-pickup devices of a television camera includes, as disclosed in, for example, JP-A-10-98651, optical means for irradiating a photoelectric conversion plane of solid-state image-pickup devices with an optical image from an object to be imaged at every first period, means for reading out electric signal charges of the solid-state image-pickup devices at every second period shorter than the first period, storage means for holding electric signal charges produced from the solid-state image-pickup devices as a reference signal when the photoelectric conversion plane of the solid-state image-pickup devices is not irradiated with the optical image due to a difference between the first and second periods, and means for correcting an image signal constituted by the electric signal charges produced from the solid-state image-pickup devices in accordance with the reference signal when the photoelectric conversion plane of the solid-state image-pickup devices is irradiated with the optical image.
According to the above conventional technique, in the same way as a black reference signal is inserted between picture signals by using a rotating shutter disk or electronic shutter, the picture signals can be produced from the solid-state image-pickup devices. As described in the above publication, in a defective pixel correcting circuit, a digitized signal is written in a frame memory as a reference image of a corresponding field during a reference signal term. During other term excepting the reference signal term, a corresponding field image stored in the frame memory is subtracted from the digitized field signal to be produced, so that a defective pixel is corrected while noise having a fixed pattern is detected in real time to thereby eliminate preparation work of defective-pixel data upon fabrication and even if a defective pixel is changed in use, an automatically corrected image can be acquired to improve the image quality.
With such structure, however, a pause period is produced in an output signal of the defective pixel correcting circuit. Accordingly, when a moving picture is to be viewed in real time, it is necessary to obtain a video signal having a continuous time interval by passing the output signal through a time-axis expansion circuit. However, in order to adjust a timing by the time-axis expansion circuit, a considerably large-scale circuit configuration must be provided to thereby increase a cost.
Further, since the video signal corresponding to the aforementioned pause period is not imaged, the contents of the picture are interrupted at the pause period and there is a possibility that the contents of the picture become discontinuous as compared with the required contents of the picture even if the time axis is expanded regardless of the interruption of the contents to make the time interval continuous.